1. Field of Invention
The present invention is in a field related to application of electricity transmission technology of an electric power system. And more particularly, the present invention relates to a method for vertically grounding and leading down form an outer side of a composite pole tower and pole tower thereof.
2. Description of Related Arts
Pole towers are important instruments in an electric transmission line. The property of material of pole powers has a direct influence on safety, economy, and reliability of operation of the electric transmission line. Since raw steel material has a high intensity and good weight ratio, pole powers of high voltage electric transmission line at home and abroad are mostly made of raw steel material. However, pole powers of raw steel material also have disadvantages such as being massive (density of the raw steel material is high) and easy to corrupt. And thus a lot of manpower and materials are required for construction, transport and maintenance of the pole towers. With the development of the composite materials, advantages such as light weight, high intensity, corrosion-resistant, bearable in high temperature and low temperature, durable, and good insulating property have been found in composite materials. Therefore, poles powers of composite material, which have advantages such as low cost of transporting (especially in a sparsely populated area), antifouling, corrosion-resistant and the like, have good utilication prospects. It should be noted that pole towers of composite material have already been widely used in some areas in Canada and America.
However, lightning protection is not an issue when the pole towers of composite material are used in Canada and America. The mainly reason is that these areas using pole towers of composite material do not suffered a lot from lightning (For these areas in Canada and America have long winters, and lightning days are very few). Furthermore, the electric transmission lines are of low voltage which is mostly lower than 110 kv and do not required grounding. In addition, influence of lightning on the system is not vital because the voltage is relatively low.
Recently, pole towers in China are made of reinforced concrete, wood or raw steel (a pole tower in the rank of high voltage which is more than 110 kv often is made of raw steel). Because of the outstanding property of composite material, many regions in China also begins to use composite material (for pole towers in the rank of high voltage which are more than 110 kv). However, in these regions of China, issues such as much efforts have been put on building the transmission corridor, lightning takes place frequently, and contamination should be concerned, so that when the pole towers of composite material are employed to these regions, focus should be put on reducing a width of the transmission corridor (reduce the maximum distance between the leads of the transmission line), avoiding damage by lightning (reduce the possibility of destroy by lightning), and preventing contamination (reduce the possibility of running out of order because of pollution flashover by increasing a climbing distance of the the pollution flashover).
In order to prevent the pole towers from damage by lightning, ground wires should be installed to the transmission line (the pole towers in Canada and America have not been provided with ground wires because it is not a issue in these regions of these countries). The pole towers of composite material should be grounded to release lightning energy of the ground wires (lightning conductor) or tower peak during lightning so as to increase ability lightning protection of the pole towers.
Therefore, in a region in which lightning takes place frequently, grounding should be carefully taken in consideration when pole towers of composite material are applied in use (since the body itself of a steel pole tower is a metal conductor, ground wires are directly electrically connected to the earth through the body of the pole tower, so that grounding is not an issue for a steel pole tower). There are several kinds of grounding and leading-down methods which directly have influence on performance of lightning protection, reducing the width of the transmission line and contamination prevention, so that methods of grounding and leading-down are important and key issues that should be solved when the pole towers of composite material are in application.